Per https://twitter.com/dhh/status/1032050325513940992, I'd like for Rails to set a good example and tone by using better terminology when we can. An easy fix would be to replace our use of whitelist with allowlist and blacklist with denylist.

We can even just use them as verbs directly, as we do with the former terms. So something is allowlisted or denylisted.

I took a quick look and it seems like this change is mostly about docs. We only have one piece of the code that I could find on a search that uses the term whitelist with enforce_raw_sql_whitelist. Need to consider whether we need an alias and a deprecation for that.